In the manufacture of paper products, such as facial tissues, bath tissues, napkins, wipes, paper towels, etc., it is often desired to optimize various properties of the products. For example, the products should have good bulk, a soft feel, and should have good strength. Unfortunately, however, when steps are taken to increase one property of the product, other characteristics of the product are often adversely affected.
For instance, it is very difficult to produce a high strength paper product that is also soft. In particular, strength is typically increased by the addition of certain strength or bonding agents to the product. Although the strength of the paper product is increased, various methods are often used to soften the product that can result in decreased fiber bonding. For example, chemical debonders can be utilized to reduce fiber bonding and thereby increase softness. Moreover, mechanical forces, such as creping or calendering, can also be utilized to increase softness.
However, reducing fiber bonding with a chemical debonder or through mechanical forces can adversely affect the strength of the paper product. For example, hydrogen bonds between adjacent fibers can be broken by such chemical debonders, as well as by mechanical forces of a papermaking process. Consequently, such debonding results in loosely bound fibers that extend from the surface of the tissue product. During processing and/or use, these loosely bound fibers can be freed from the tissue product, thereby creating lint, which is defined as individual airborne fibers and fiber fragments. Moreover, papermaking processes may also create zones of fibers that are poorly bound to each other but not to adjacent zones of fibers. As a result, during use, certain shear forces can liberate the weakly bound zones from the remaining fibers, thereby resulting in slough, i.e., bundles or pills on surfaces, such as skin or fabric. As such, the use of such debonders can often result in a much weaker paper product during use that exhibits substantial amounts of lint and slough.
As such, a need currently exists for a paper product that is strong, soft, and that has low lint and slough.
In accordance with one embodiment of the present invention, a paper product is formed from at least one paper web. In particular, the paper web includes hardwood fibers (e.g., eucalyptus fibers). At least a portion of the hardwood fibers are treated with a first hydrolytic enzyme capable of hydrolyzing the hardwood fibers to form aldehyde groups predominantly on the surface of the hardwood fibers. For example, in some embodiments, the dosage of the first hydrolytic enzyme is from about 0.1 to about 10 s.e.u. per gram of oven-dried pulp.
In addition, in some embodiments, the paper web can also include other types of fibers, such as softwood pulp fibers. In one embodiment, at least a portion of the softwood fibers are treated with a second hydrolytic enzyme capable of randomly hydrolyzing the softwood fibers to form aldehyde groups predominantly on the surface of the softwood fibers.
The enzyme-treated fibers can provide additional strength to the paper web such that lint and slough can be minimized. In addition, other ingredients, such as cross-linking agents, debonders, strength agents, and the like, can also be utilized to form paper webs having certain attributes. For instance, the above-mentioned additives can be applied to the first layer, second layer, and/or third layer of a multilayered paper web.
For example, in some embodiments, a cross-linking agent containing two or more hydroxy moieties can be used to form glycosidic bonds with the aldehyde groups formed predominantly on the surface of the cellulosic and/or hemicellulosic fibers. For instance, one or more starches may be utilized to form glycosidic bonds with the aldehyde groups. In some embodiments, natural or modified starches can be utilized. One such commercially available starch can be obtained from National Starch and Chemical Company (Bridgeport, N.J.) under the trade designation xe2x80x9cRedibond 2380Axe2x80x9d.
As stated above, a debonder may also be applied to the paper web. In some embodiments, the debonder can be applied in amounts up to 35 pounds per metric ton of total fibrous material (lb/MT), particularly between about 1 lb/MT to about 10 lb/MT, and more particularly between about 2 lb/MT to about 8 lb/MT.
In general, any material that can be applied to cellulosic fibers or a paper web and that is capable of enhancing the soft feel of a paper product by disrupting hydrogen bonding can generally be used as a debonder in the present invention. For instance, one commercially available imidazoline debonder is available from McIntyre Group, Ltd. under the trade designation xe2x80x9cMackernium DC-183xe2x80x9d.
If desired, a strength agent (i.e., wet-strength or dry-strength) can also be utilized, in some embodiments, to further increase the strength of the paper product. For example, in some embodiments, the strength agent can be applied in amounts up to 20 pounds per metric ton of total fibrous material (lb/MT), particularly between about 1 lb/MT to about 10 lb/MT, and more particularly between about 2 lb/MT to about 6 lb/MT. One commercially available wet strength agent, for example, that can be used in the present invention is xe2x80x9cKymene 557LXxe2x80x9d, which is sold by Hercules, Inc.
Additives, such as described above, can generally be applied at various of stages of a papermaking process. For instance, in some embodiments, the additives can be applied prior to forming the web (i.e., added to the pulper, dump chest, machine chest, clean stock chest, low density cleaner, added directly into the head box, etc.). Moreover, if desired, the additives can be applied after web formation as well (i.e., onto the web after being deposited by the headbox, onto a forming or transfer fabric or felt, at the drier, the during the converting stage, etc.). For instance, in one particular embodiment, an additive, such as a debonder, can be applied to a dryer drum such that the additive is transferred to the web when the web traverses over the drum during drying.
Other features and aspects of the present invention are discussed in greater detail below.